Externally finned hermetic compressor



Jan. 3, 1950 J. TQUBQR'G EXTERNALLY FIHN'BU HBRIETIC COIIPRESSOB Filed May 20, 1947 2 Sheets-Sheet 1 Patented Jan. 3, 1950 EXTERNALLY FINN ED HERMETIC COMPRESSOR Jens Touborg, Tecumseh, Mich., assignor to Tecumseh Refrigeration Salesand Engineering Company, Tecumseh, Mich., a corporation of Michigan Application May 20, 1947, Serial No. 749,318

1 Claim. 1

This invention relates to hermetic or hermetically sealed compressors of the type utilized in refrigerating machines, and it has particular reference to the provision of fins, or secondary heat radiating surface, on the casing of such compressor, in such manner as to improve the effectiveness thereof.

It has heretofore been proposed to enclose the motor and compressor for a refrigerating machine in a sealed casing, and compressors of this nature are commonly called hermetically sealed or hermetic compressors. Inasmuch as such devices have been widely used and are well understood, it is deemed unnecessary in this specification to discuss their construction and mode of operation at length. Briefly, the hermetic compressor unit is connected to discharge hot compressed refrigerant to a condenser, from whence the refrigerant flows to an evaporator to produce its refrigerating effect, and. then is returned in gaseous form tothe compressor for recycling. The act of compression produces heat, and therefore some provision must be made for dissipating that heat from both the compressor and condenser. One common method has been to provide an auxiliary fan to force a draft of air,- at fairly high velocity, over the surface of the compressor casing, as well as the refrigerant con denser.

In certain installations of refrigerating machinery for such uses as domestic boxes and the like, recourse is made to what may be termed a natural convection method of cooling. That is to say, the auxiliary fan is omitted, and natural convection of air around the high side units (1. e.,

compressor and condenser) is relied upon to remove sufdcient heat of compression to maintain the equipment at a proper temperature range. Due to the slower movement of the air in this instance, the same rate of heat transfer is not obtained, as with the forced draft or fan method.

Machines operating on the natural convection principle, or as static systems as they are sometimes referred to, have therefore been provided with external fins Welded to the surface of the compressor casing or shell. It has long been known and accepted as axiomatic that the greater the amount of fin surface, or-indirect surface, the greater is the total radiating surface in contact with the cooling air. Accordingly, it has been reasoned that by providing a very extensive secondary or indirect radiating surface on the hermetic casing, the rate of heat dissipation could be proportionately increased. The practice has therefore been to cover as'much as possible of the casing surface with the fins, and, as a means to obtain good transfer between the casing and fins, to unite the two by welding along the areas of contact.

I have now discovered, however, that superior results may be obtained by what may appear to be a definite departure from these accepted practices. That is to say, for hermetic compressors intended for use in static systems, I find that a more efi'ective'cooling of the compressor can be obtained if the secondary surface of radiation is limited in its extent and its location on the shell. I have moreover found a new and simplified way to apply such radiating surface to the shell, which results in economies of manufacture, lessens danger of damage to the compressor, and generally results in an improved article of manufacture.

For the purposes of this description, reference may be made to my prior patent, No. 2,364,038, of November 28, 1944, wherein I have described, among other things, a hermetic compressor including a motor and compressor enclosed in a sealed casing, and mounted therein in spaced relation to the internal walls of the shell by means of resilient supports. In this type of unit, there is only a very small metallic path between the motor and compressor, wherein the heat is generated, and the casing wall, through which such heat must be dissipated. Performance data hereinafter referred to are predicated on a unit of this nature, but it is to be understood that like results are obtainable on other types of units, and that this reference is made for explanatory purposes.

The nature of the present invention will be explained in the following description by reference to the appended drawings, wherein:

Fig. 1 is a plan of a hermetic compressor incorporating the invention;

Fig. 2 is a side elevation thereof, the motor and compressor being indicated in dotted lines;

' Fig. 3 is a fragmentary section, further showing some of the internal elements of the machine;

Fig. 4 is an enlarged sectional detail of the retaining means for the improved radiating surface; and,

Fig. 5 is a chart showing, by comparison, the improved heat transfer effects obtained by the invention.

In Figs. 1, 2, and 3, there is shown a hermetic compressor having a casing it, initially formed as upper and lower shells i2 and it, which are later welded together along abutting flanges It to seal the unit. An electric motor i 5 is mounted in a supporting frame I 6, and its shaft is coupled 'to a compressor I! wherein the refrigerant is 22 contained in the lower shell, and which may properly be of suflicient depth to inundate the lower part of the compressor I'I.

The casing I I may be mounted on any suitable supporting platform by means of pads 2II..the casing portions I 2 and I3 may be given whatever contour or shape is desired -and'a:starting ca pacitor 24 may be secured to the external wall of the casing as a matter of convenience. No claim is made herein to any patentable novelty in the structure thus far enumerated, ='as"it has all been presented heretofore in the literature.

Referring further-toFigs. -l, 2, and 3, it will be'seen' that the lower pontion of the external surface "of thecasingll is providedwith addrtional radiating surface 25, which surface is utilized to provide for heat transfer to the. surrounding air. The upper portion of-the casing is not so equipped,.however,-and herein the present invention presents a materi'a1 point of distinction to the customary prior' art practices.

Further according to this invention, the surface 25 advantageously takes the form of acorruga-ted and continuous strip of metal, formed into outstandingflange sections 26 which are connected at their outermost ends by return bends 21, and which are connected'at their inner endsby contiguous shell engaging portions 28. The'band ofmetal is alsobent into a generally circumferential shape, suited to the periphery of the shell I3, sothat, wh'en"'it is wrapped or positioned around it, the portions 28 will fit against the shell wall with as full contact as is practicable.

The return bend portions '21 are also notched along the medial line of the metal, as indicated b the reference numeral .29. These notches are adapted to receive an encircling band or strap 3|, whose ends are formed with right and left hand threads 32 and 33, to receive the tapped portions of a turnbuckle 34. As further shown in Fig. 4, when the strap 3i is placed in the notches 29, and the turnbuckle 34 taken up, the surface 25 is 'tightlysqueezed against the casing, the portions .28 being pressed against the shell section l3. If desired, the portions 28 may, prior to assembly, be coated with what is known in the trade as cold solder, which isa plastic composition suited to make a. light heat. conducting bond between the parts so contacted.

The preferred modeof fabrication should now be apparent. the usual way, as though it were to be employed without anysecondary radiating surface. Thereafter the preformed band of metal 2.5.is placed around the lower shell I3, and the turnbuckle 3 is taken up to strap-'the-surface 25 tightly to the shell. This procedure eliminates weldin operations, as have heretofore been used, and which are cumbersome and potentially injurious to the equipment, whether the welding be done beforeor after the'closing of the casing. Compressive forces applied to the ends of the flanges 26 which are disposed substantially radially t the shell-:13, aretransmitted-totheshell or pad EQI iiOBS. 2.8, toprovidetight frictionalengage- The compressor is put together in 4 ment preventing the slipping of the surface from the shell.

It will accordingly be seen that there has been provided a simplified indirect radiating surface for the compressor casing, through which the heat transmitted to the casing wall may be further conducted and dissipated. As shown in Figs. 1 and 3, the gaps between adjacent fins or flanges 26 and the casing wall provide small lines 35, through which cooling air may flow by induced draft or convection. As the air flows over the surfaces, the heat is transferred there- --to, thus maintaining the compressor at a suitable operating temperature. i

.As"heretofore noted, it has previously been customary 'to extend the secondary radiating surface over the entire casing, as, for example, by continuing the surface over the upper shell I21 However, by restricting the surface 25 to a portion of the shell, as hereindescribed, a surprisingly increased effectiveness of heat transfer is; now-obtainable. This may be further considered with reference to Fig. 5.

.In the diagram, the effectiveness of heat transfer is shown by plotting the external surface temperature of the casing against the-evaporating temperature on the low side of the system. The tendency is for the surface temperature to rise with the evaporating temperature, inasmuch as low evaporating temperatures return the expended refrigerant at alower density, and thereby provide an internal or intrinsic way of reducing the heat content. The dotted curves A and- B are, respectively, surfacetemperatures of the lower and upper "shell sections I3 and I2, when each .is provided with radiating surfaces. as has been common inthe prior art, and wherein such surfaces have been welded to the shells.

The solid line curves C and D respectively represent the lower and upper shell temperatures, under comparable conditions of operation, for a compressor embodying the present invention. It will be seen that curve C is considerably below curve A, showing that the improved radiating surface dissipates more heat.

Likewise, while the gap between curves B and D is not so pronounced, it is clear that with the present invention, the upper shell is maintained at a lower temperature than it was when provided with indirect surface.

Moreover,-the prior art type, as shown by curves A and B, had a total indirect radiating surface of over twenty per cent more than the improved unit, whose performance is shown by curves C and D. That is to say, the improved results have beenobtained by employing less indirect surface, with'a consequent saving of material, as well as increased effectiveness of operation.

While the results are as stated, and are existent independent of any theory, it may be suggested that when the surface is extended over the entire casing, the lengths of the flues 35 is such that airflow therethrough is impeded, rather than accelerated. Further, it will be seen from Figs. 3 and 5 that the; upper shell section I2 is substantially spaced: 'from the working parts, while the lower shell I3 is in contact with the oil bath 22-,- so that most of the heat generated is transmitted through the bath, and therefore the lower shelltemperature, in both instances, is greater. Obviously,- therefore, the reduction of the lower shell temperature, as herein obtained, effects heat'removal more directly from the region ,of. its. transfer to the casing-wall. Reduction of the length of the .fiues 35 moreover appears to increase the velocity of the air, as shown by the concurrent reduction of the upper shell temperature.

It will accordingly be seen that the present invention provides a simplified and improved form of hermetic compressor having indirect radiating surface thereon. While the invention has been described with respect to a preferred embodiment, and has been explained with reference to certain test data, it will of course be understood that it is not limited to the illustrative examples given, but should be deemed to have a scope commensurate with the import of the following claim.

I claim:

A hermetically sealed compressor unit comprising a fluid tight casing, a compressor disposed within said casing adjacent one end thereof, a driving motor for said compressor disposed in said casing adjacent the opposite end thereof, means for facilitating the dissipation of heat generated by said compressor comprising an endless flexible band of corrugated sheet metal disposed about the portion of said casing housing said compressor with the corrugations disposed longitudinally of said casing, and with the inner ridge of each corrugation in intimate contact REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,873,670 Steenstrup Aug. 23, 1932 2,071,870 Ballentine Feb. 23, 1937 2,243,466 Kucher May 27, 1941 FOREIGN PATENTS Number Country Date 38,249 France Jan. 27, 1931 

